ATM assignment

My teacher just gave us an ATM assignment and today was our 4 week of programming , our teacher hasnt taught us about file linking or stuff , i wanted to ask that the problem which il be having is that my teacher told us that .

"When your program starts, it should be displaying a login screen. User will be asked to enter a login and 5 digit pin code. The system verifies the login and pin and displays an error if it is incorrect
You have to create a array that holds the username and password
Enter login: example
Enter Pin code: 12345 "

I dont know how how will i save the data of a user :$ , when it will ask login or stuff ? how can it be done ? storing data in a text file and then accessing it , please help me out with that part

http://www.cprogramming.com/tutorial/lesson1.html

It seems to me you don't have to store anything in a file. The assignment states you just store it in an array, so it sounds to me like you hardcode it in the application...